FC5->Ubuntu

I currently have ZCS 4.5 running on a Fedora Core 5. I am working on changing my servers to Ubuntu. I want to install ZCS 5.x. I am aware that I cannot just copy my existing directories over to the new server, different libraries, etc.
However to set up a new mail server is going to require I have cname and MX.
I do not have one for the ubuntu server yet, as my plan is to rename the server to the current mail server name after testing is complete and if successful.

Question 1. LDAP, I have ldap running on the FC5 computer, can I migrate all the users over the ubuntu server?

Question 2. Mail, can I copy the mail directory over to the new ubuntu server?

Question 3. Is there I way around setting/changing the server name after Zimbra is up and running?

Ubuntu 8.04

I see installing zimbra on ubuntu 8.04 is a real hassle or not even possible.
I hate to install it on 6X because the next thing you know they will stop supporting 6x then I need to do a new upgrade in 3 months anyhow. I had it on FC5 but now you cannot install it on fc5
Has anyone had any success on ubuntu 8.04?
Thanks